1. Field of the Invention
The present invention relates to an optical option attachment ring, and in particular, to an optical option attachment ring which has the same substantially cylindrical contour as a lens barrel and no projection.
2. Description of the Related Art
An optical option attachment ring for mounting a wide-angle converter and teleconverter on a lens barrel has been known hitherto (refer to, for example, Japanese Patent Application Laid-Open No. 2004-271892).
An optical option attachment ring according to Japanese Patent Application Laid-Open No. 2004-271892 is described below with reference to a drawing. As illustrated in FIG. 7, the optical option attachment ring 10′ includes one end 21′ and the other end 22′ arranged at predetermined spaced intervals, a ring body 20′ which couples the one end 21′ to the other end 22′ and into which a lens barrel (not shown) is inserted, and a fixing screw 23′ which is inserted into screw holes 21a′ and 22a′ causing the one end 21′ to communicate with the other end 22′. In the optical option attachment ring 10′, the fixing screw 23′ is fastened to cause the one end 21′ to be close to the other end 22′ to decrease the ring body 20′ in diameter, fixing the ring body 20′ to the lens barrel and the fixing screw 23′ is loosened to cause the one end 21′ to be apart from the other end 22′ to increase the ring body 20′ in diameter, releasing the fixing.
As illustrated in FIG. 7, the one end 21′ and the other end 22′ of the optical option attachment ring 10′ are slanted. Fastening the fixing screw 23′ causes a portion 22b′ of the other end 22′ to move along the slant face of the one end 21′ and project inside the inner surface 20a′ of the ring body 20′ and be positioned in (be engaged with) a groove (not shown) formed in the lens barrel. This prevents the optical option attachment ring 10′ from falling off the lens barrel even if the fixing screw 23′ loosens.